Conventionally, vascular grafts with diameters greater than 6 millimeters, fabricated from a variety of synthetic materials, have been successfully used for a number of years in reconstructive surgery. The same degree of success has not been achieved with conventional grafts having diameters smaller than 6 millimeters.
Certain characteristics are recognized as necessary for artificial vascular grafts. The graft must have such physical properties that it can be readily handled and manipulated during the specific surgery calling for its use. It must be flexible as it is sometimes necessary in surgery to bend a graft around or under a body organ. A prosthesis will, of course, be required to flex within the human body in which it is implanted. While flexible, it must nonetheless have a certain rigidity so as to prevent collapse or kinking with subsequent closing of the passageway. The prosthesis should maintain its strength and flexibility permanently.
Additionally, a prosthesis should be non-toxic and acceptable to body tissues and fluids. A vascular graft in particular must be biocompatible to blood, and surfaces interfacing with blood must be thromboresistant. An effective prosthesis should also be porous, avoid the formation of fluid pockets, and promote the growth through the fabric of repair tissue.
Tubes of fabric have been found to be useful as cardiovascular grafts. Fabric tubes can be assured to be biocompatible with blood by coating the interior surface of the tube with carbon, as described in U.S. Pat. application Ser. No. 813,538, filed July 7, 1977, in the name of Jack C. Bokros, now U.S. Pat. No. 4,169,477.
A spring inserted inside a fabric tube adds strength to the tube and permits greater flexing without kinking.
An example of such a spring used to strengthen a fabric prosthesis is taught in U.S. Pat. No. 4,130,904 issued Dec. 26, 1978, to Robert L. Whalen, which shows a spring frictionally engaged between two concentric fabric tubes. The inside surface of the inner tube is designed so that a thin layer of blood will coagulate thereon thus coating the interior surface. Because of the configuration of concentric tubes, air pockets exist between the fabric tubes into which blood can seep and therein coagulate. It is the property of blood that coagulated blood can hasten further coagulation of blood and, therefore, a prosthesis which relies on blood coagulation to form a biologically integrated surface may lead eventually to sufficient buildup of coagulated blood to hinder blood flow. It would therefore be desirable to have a surface which is biocompatible without relying on coagulation and which eliminates pockets in which clots can begin. To this end the use of springs is taught in the instant invention which are in themselves biocompatible and thromboresistant and which either in themselves or in conjunction with a single biocompatible and thromboresistant layer of fabric join segments of blood vessels.
Accordingly, it is an object of this invention to provide strong flexible and durable cardiovascular prostheses which will not kink or collapse through the use of springs which are biocompatible and thromboresistant.
It is a further object of this invention to provide improved blood compatible surfaces for vascular grafts in which the surfaces are well washed by flowing blood so as to prevent blood clotting.